Trochlear Dysplasia

The investigators intend to establish a national cohort including all persons in the ages from 15-20 years old with patellar instability (PI) or a prior knee injury (ACL-ruptur or meniscus damage) . The cohort will be nicknamed "The Faroese Knee Cohort". The overall aim is to investigate two groups. 1. The patella instability group, in which we intend to investigate the following. * Prevalence of patellar dislocation and trochlear dysplasia in the Faroe Islands. * Risk factors for patellar dislocations- * Heredity of trochlear dysplasia. * If there is a specific gene responsible for the development of trochlear dysplasia. * The development of retropatellar artrhosis, its onset and its impact on quality of life and function, 2. Knee injury group (ACL-ruptur or meniscus injury) * The prevalence of ACL-rupture and/or meniscus injury in this specific group in the Faroe Islands. * The impact on quality of life and function.